The present invention concerns methods of making integrated circuits, particularly methods of making metal masks and dielectric, or insulative, films.
Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators typically build the circuits layer by layer, using techniques, such as doping, masking, and etching, to form thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.
One important concern during fabrication is flatness, or planarity, of various layers of the integrated circuit. For example, planarity significantly affects the accuracy of a photo-imaging process, known as photomasking or photolithography, which entails focusing light on light-sensitive materials to define specific patterns or structures in a layer of an integrated circuit. In this process, the presence of hills and valleys in a layer forces various regions of the layer out of focus, causing photo-imaged features to be smaller or larger than intended. Moreover, hills and valleys can reflect light undesirably onto other regions of a layer and add undesirable features, such as notches, to desired features. These problems can be largely avoided if the layer is sufficiently planar.
One process for making surfaces flat or planar is known as chemical-mechanical planarization or polishing. Chemical-mechanical planarization typically entails applying a fluid containing abrasive particles to a surface of an integrated circuit, and polishing the surface with a rotating polishing head. The process is used frequently to planarize the insulative, or dielectric, layers that lie between layers of metal wiring in integrated circuits. These insulative layers, which typically consist of silicon dioxide, are sometimes called intermetal dielectric layers. In conventional integrated-circuit fabrication, planarization of these layers is necessary because each insulative layer tends to follow the hills and valleys of the underlying metal wiring, similar to the way a bed sheet follows the contours of whatever it covers. Thus, fabricators generally deposit an insulative layer much thicker than necessary to cover the metal wiring and then planarize the insulative layer to remove the hills and valleys.
Unfortunately, conventional methods of forming these intermetal dielectric layers suffer from at least two problems. First, the process of chemical-mechanical planarization is not only relatively costly but also quite time consuming. And second, the thickness of these layers generally varies considerably from point to point because of underlying wiring. Occasionally, the thickness variation leaves metal wiring under a layer too close to metal wiring on the layer, encouraging shorting or crosstalking. Crosstalk, a phenomenon that also occurs in telephone systems, occurs when signals from one wire are undesirable transferred or communicated to another nearby wire.
Accordingly, the art needs fabrication methods that reduce the need to planarize intermetal dielectric layers, that reduce thickness variation in these layers, and that improve their electrical properties generally.
To address these and other needs, the inventor devised various methods of making dielectric layers on metal layers, which reduce the need for chemical-mechanical planarization procedure. Specifically, a first exemplary method of the invention forms a metal layer with a predetermined maximum feature spacing and then uses a TEOS-based (tetraethyl-orthosilicate-based) oxide deposition procedure to form an oxide film having nearly planar or quasi-planar characteristics. The exemplary method executes a CVD (chemical vapor deposition) TEOS oxide procedure to form an oxide layer on a metal layer having a maximum feature spacing of 0.2-0.5 microns.
A second exemplary method includes voids within the oxide, or more generally insulative, film to improve its effective dielectric constant and thus improve its ability to prevent shorting and crosstalk between metal wiring. Specifically, the exemplary method uses a TEOS process at a non-conformal rate sufficient to encourage the formation of voids, and then uses the TEOS process at a conformal rate of deposition to seal the voids. More generally, however, the invention uses a non-conformal deposition procedure to encourage formation of voids and then a more conformal deposition to seal the voids.
A third exemplary method increases the metal-fill density of metal patterns to facilitate formation of intermetal dielectric layers having more uniform thicknesses. The third exemplary method adds floating metal to open areas in a metal layout and then extends non-floating metal dimensions according to an iterative procedure that entails filling in notches, and corners and moving selected edges of the layout.